Cellular and humoral immune responses of germfree and convential mice and rats to a variety of viable and nonviable antigens will be studied. The ability of germfree animals, and gnotobiotic animals monoassociated with bacteria, to mount cell-mediated immune responses and to demonstrate delayed hypersensitivity will be studied. BIBLIOGRAPHIC REFERENCES: Carter, P.B. 1976. The use of mice in assessing the protective and immunopotentiating capacity of BCG vaccine administered orally. Am. Rev. Resp. Dis. 113:154a. Cassell, G.H., P.B. Carter, and S. Silvers. 1976. Mycoplasma pulmonis genital tract disease in rats - development of an experimental model. Proc. Soc. Gen. Micro. 3:150.